1. Field of the Invention
The invention relates to an inkjet recording apparatus which includes a nozzle and an actuator, and ejects an ink droplet from the nozzle onto a recording medium by driving the actuator, thereby recording an image or information on the recording medium.
2. Description of Related Art
As a kind of an inkjet recording apparatus of this type, the publications 1-4 set forth below disclose apparatuses that control printing of dots in order to prevent blurring or spreading of ink that is a phenomenon that when a droplet of ink is ejected onto a recording medium to form a dot on an outline of an image recorded on the recording medium, the ejected ink droplet grows or spreads on the recording medium into a white, non-recording area in the recording medium, thereby increasing the size of the dot. This phenomenon will be hereinafter referred to as “dot growth”. The prevention of the dot growth is essential particularly in recording apparatuses for recording codes such as one-dimensional or two-dimensional barcodes, such as those apparatuses disclosed in the publications 1 and 3, since a misreading of a barcode should not occur.                Publication 1: JP-A-2003-237059        Publication 2: JP-A-2002-292848        Publication 3: JP-A-2000-103042        Publication 4: JP-A-2003-285453        
Each of the recording apparatuses disclosed in the publications 1-3 is constructed to print a single dot by ejecting a single ink droplet from a nozzle onto a recording medium, and to print an outline of an image by ejecting small ink droplets each of which is smaller in volume than ink droplets ejected for forming the other part of the image than the contour or outline. According to this arrangement, a size of a single dot formed on the recording medium depends on a volume of a single ink droplet. Hence, a variation in volume of ink droplets significantly affects the uniformity in shape, size and density of the dots formed by the ink droplets on the recording medium, thereby deteriorating the quality of the image at the outline thereof
Meanwhile, the recording apparatus disclosed in the publication 4 is constructed to print an outline of an image by forming dots each of which is formed by a single ink droplet, and print the other part of the image by forming dots each of which is formed by two or three ink droplets. Both of the outline and the other part of the image are printed according to a drive waveform signal consisting of a series of pulses that form a waveform. More specifically, timing signals are inserted in the common drive waveform signal at suitable timings to divide the drive waveform signal to provide three kinds of signals of respective waveforms, as needed. That is, a first kind of drive waveform signal for ejecting a single droplet, a second kind of drive waveform signal for ejecting two droplets, and a third kind of drive waveform signal for ejecting three droplets, are provided by dividing the common drive waveform signal with the timing signals. However, after ejection of an ink droplet or ink droplets, a change in ink pressure remains in an ink passage, an end of which constitutes a nozzle, and the state of the remaining change in the ink pressure varies in a manner depending on the number of ink droplet or droplets having been ejected in series. Hence, the different kinds of drive waveform signals respectively for ejecting one, two and three ink droplets in series, which signals are obtained by simply segmenting the common drive waveform signal with the timing signals can not apply to the ink, energy of a level appropriate for ejecting each number of ink droplet or droplets. Accordingly, at the outline of the recorded image, the print quality is relatively low.
Thus, any of the recording apparatuses disclosed in the publications 1-4 succeeds in accurately controlling the size of printed dots, that is, dots at an outline of an image recorded by the recording apparatuses may enlarge or grow to degrade the print quality.